The present invention relates generally to the preparation of inorganic samples by fusion and, more particularly, concerns an improved method and system for the preparation of inorganic samples by fusion.
In a known, existing process for the preparation of inorganic samples for analysis, the sample (geological, mineralogical or some inorganic material) in powdered form is mixed with a powdered reagent called a flux. The mixture is placed in a platinum-gold alloy crucible, and heated to a temperature slightly above 1000° C. At such temperatures, the flux will melt in a few minutes and dissolve the oxides present in the sample, producing a homogenous mix. This molten mix is then poured into a mold made of the same alloy as the crucible. Upon cooling, the material in the mold will solidify, resulting in a glassy disk that can be analyzed.
This process exhibits at least the following shortcomings:                In some instances this procedure can take an inordinately long time;        The cost of the crucibles and molds is very high, these items being made of precious metals;        With some samples, the molten material is very sticky, and causes the glassy disk to crack;        The melt stickiness can also cause fast mold degradation;        The surface of the mold must be as perfectly flat and as smooth as possible or analytical errors will appear;        Re-polishing of the mold surface is needed to maintain this smoothness;        Samples containing platinum or gold (or other precious metals) cannot be prepared, due to the risk of amalgamation with the crucible.        
Broadly, it is an object of the present invention to provide a method and system for the preparation of inorganic samples, which overcome one or more of the shortcomings of the existing process. It is specifically contemplated that the method and system should be convenient and reliable in use, and preferably should realize cost savings in comparison with the existing process.
In accordance with one aspect of the invention, a smooth receiving surface for the mix is ensured and the amount of surface re-polishing minimized by pouring the homogenous mix on an inert, molten metal surface, such as liquid gold.
In accordance with another aspect of the invention, the speed of the process is improved by pre-melting the flux in a heating chamber and mixing it with the sample in a liquid state. It is also contemplated that the speed of the process can be increased by cooling the glassy disk with a fluid that has a substantially higher thermal capacity than air, which is normally used for cooling. Preferred fluids include water and liquefied gases, which are very cold when depressurized from their stored form to atmospheric pressure.
In accordance with another aspect of the present invention, savings can be realized by eliminating crucibles made of precious metals (e.g. a platinum-gold alloy, hereafter also referred to as “platinumware”) and replacing them with crucibles made of a glassy graphite (hereafter also referred to as “graphiteware”). However, inasmuch as graphite degrades quickly at high temperatures in the presence of oxygen, the process must be performed in an inert gas ambient atmosphere, preferably one containing nitrogen, argon, or neon, or combinations thereof